Trunking system



Sept. 15,1931. A. c. POWELL 1,823,667

TRUN ING SYSTEM Filed Sept. so. 1930 4 Sheets-Sheet 1 /NVEN7'0/? A. 6! P0 WELL A rom/5r Sept. 15, 1931.

A. C. POWELL TRUNKING SYSTEM Filed Sept., 30. 1930 4 Sheets-Sheet 2 A 7' TURNEY Sept A. C. POWELL TRUNK'ING YsTEM Filed Sept. 50. 1930 4 Sheets-Sheet a A] INVENTUETA A. G. POWELL POSITION SPL/ TT/IVG C I PCU/ Tx Sept. 15, 1931. A. c. POWELL TRUNKING SYSTEM Filed Sept. 30. 1930 4 Sheets-Sheet 4 )4 T TOEWE Y Patented Sept. 15, 1931 hairs stares PATENT OFFICE ALBERT c. rownnn, on NEW YORK, n. Y., ASSIGNORTO BELL return own LABORATO- g REES, INOORPUBATED, F NEVI YGRK, N Y., A. CORPORATION, OF NEW. YORK TR-UNKING- sYs'rE-M Application filed September 30, 1930. Serial No. 485,423;

This invention relatesto telephone systems i in which connections are established under the control of operators and has for its ob ject increased rapidity and efficiency in the direction of calls to an operator for extension. The invent-ion finds specific embodiment in asystem in which calls incoming to an operators position are automatically and successively connected to equipment for receivfrees'the trunk after a measured length of time, while in the case of a connection eX- tended by an A operator the trunk awaits the attention of that operator; Slnce'the failure to establish this circuit may be due to transient conditions, in accordance with the present invention, when the B operator disconnects her equipment from the trunk following such a failure, the trunk is again marked as calling so that the automatic a-pparatus may subsequently make a second at- 9 tempt to connect the trunk with the operators equipment and thus permit the proper completion of the call. The same act which frees the trunk from the operators equipment serves to prepare the ringing equipment of the trunk to signal the called subscriber but where the designction is not received, the disconnection is ineffective for this purpose. The switching apparatus is also arranged to discriminate between calls incoming from operators and calls'incoming from dial otfices and in the latter case delays the establ shment of the circuit over which the designation is to be transmitted if the plug of the incoming trunk has not been removes from the jack with which it was used in connection with an earlier call.

This invention is in the nature of a modification of the svstem disclosed and claimed in Patent 1,746,793 to, W. A. Rhodes et al., issued February 11, 19 30 andreference 1s ing the designation of the Wanted line. In,

hereby made to that patent for a more complete disclosure of the system as a whole. As far as possible the same reterence'numerals have been used in the present patent as .Were'used in the Rhodes et al. patent.

In the call distributing arrangement of the Rhodes patent and the present'patent,'the trunks appearing in any position are divided into three groups. There is a group'circuit individual to each group, and a position or master circuit individual to each position, which may associate itself through a group circuit witha trunk. ,Each position, which may serve trunks incoming from a machine switching ofiice, is provided with a recorder for indicating the calledline number.- In addition each position is'provided with keys by means of'which' operators divisions of any desired size may be created. The equipment is so arranged that in general the operation of a-key permits the group circuits at from a manual or a dial oflice since trunksof both kinds may appear in'the same group. It now either associates a call indicator with the trunk causing the'sender'to send out impulses for operating the indicator in the well known manner, or it applies a tone to the trunk to indicate that the operator is ready to receive the number. As soon as the number has been received, either orally or visual lv,-the operator depresses'the release key, releasing the master circuit and group circuit 'rom the trunk. She then tests the line in the usual. manner and, inserting the plug in the line ack if the line is idle, causes ringing to take place and the connection to be completed. The operation of the release key advances the group circuit switch to the next trunk and the master circuit switch to the next group, to distribute the handling of calls among the trunks. If the designation is not received the operator may releasev the master circuit by the use of an emergency release hey whereupon the calling condition is restored to the trunk and it is reassociated with the group circuit and the master circuit for the purpose of making a second attempt at completing this connection.

A clearer understanding of the invention may be obtained from the following detailed description and the attached drawings in which:

Fig. 1 shows a subscribers line and a plug ended trunk incoming from a dial office as well as a portion of a trunk incoming from a manual office; V I

2 shows the group circuit serving the trunk of Fig. 1; and

Figs. 3 and 4 show the master circuits at the position to which the trunk of Fig. 1 and group circuit of 2 belong.

The establishment of a connection from the subscriber at machine switching substation 200 to the subscriber whose line jack is represented at 227 will i first be described. The initiation'of a connection by the subscriber at substation 200, the association of the sender 212 with the line and the selection of an idle trunk by districtselector 218 under the control of the sender 212 takes places substantially as described in U. S. patent 1,589,402 granted to Kopp, June 22, 1926.

When the trunk has been selected, the sender connects a relay across the tip and ring conductors, completing a circuit from battery through the left winding of relay 218, upper left winding of repeatingcoil 219. upper back contacts of relays 248 and 245 through the district selector 213 to the sender relay. back through the district selector, lower back contactsof relays 245 248. lower left winding of repeating coil 219; right winding of relay 21 8 to ground. Relay 218 operates closing ground at its front contact over the back contact of relay 220 to conductor 221 directly and through resistance 222 to conductor Conductor is common to all trunk circuits of the group; there being a resistance. like resistance 222 for each trunk. The grounding of conductor 223 completes a circuit through the winding of relay 410 to batterV while the grounding of conductor 221, which is individual to the trunk, marks the terminal corresponding to the trunk in the bank of brush of the group selector 400.

Relav 410 operatesto initiate the association of the group circuit with the trunk circuit by connecting ground to conductor 466 also closing a circuit from battery through the winding of relay 407. back contact of ma ggnet 408, right contact of relay 410, back contact of relay 4 12, back contact of relay 411 to ground. Relay 407 closes a circuit from battery through the winding of magnet 408, front contact of relay 407 to the operating ground for relay 407. Magnet 408 operates opening the circuit of relay 407, which releases, in turn opening the circuit of magnet 408 to release the magnet and step the brushes of switch 400 to the next terminal in search of the marked trunk. When group switch 400 finds the trunk over which the call is incoming, a circuit is completed from battery through the-winding of relay 411, left back contact of relay 413, brush 404 to grounded conductor 221.

Relay 411 in operating disconnects ground from the circuit of relay 407 to prevent the advance of switch 400 from the terminals of the calling trunk. It also closesa circuit from battery through the winding of relay 412 to ground at the left front contact of relay 411. Relay 412 closes a substitute ground to conductor 466. Relay 412 also connects battery to the winding of relay 409 the other terminal of which is connected over back contacts of relays 417 and 418 through brush 405 to conductor 224 and through the winding of relay 229 to the sleeve terminal of plug 228 to test whether or not the plug isin the jack. Relay 409 is efiectiye to prevent the call being directed to a team operator if the plug is in the jack since it holds open the circuit of relay 415 which is the teaming relay. Relay 412 also provides battery for the left winding of relay 415 the other end of which circuit extends to the position splitting circuit to determine whether or not the relay should be operated to direct the call to an adjacent position. As-

suming that the call is not to be connected to an adjacent position the circuit of this relay will not be completed and this relay may be disregarded. The operation under team work conditions is fully set forth in the above mentioned patent to Rhodes et all 1 Relay 410 in operating also closes a circuitfrom ground at its inner left front contact, inner right back contact of relay 413, through lamp 414 to battery. Lamp 414 lights indicating that a call is incoming in the group served by switch 400.

The connection of ground over the left front contact of relay 410 to conductor 460 completes a circuit extending through the splitting circuit to conductor 465, inner right back contact of relay 415, conductor 440 and thence in parallel through resistance 809 over the outer left back contact of relay 811 to battery through the winding of relay 1200, for the purpose of initiating the operation of master switch 800 and to the terminal of brush 800 corresponding to the group for the purpose of marking that group to the master switch. The operation of relay 1200 closes circuit from battery through the winding of relay 807, back contact of magnet 808, outer right front contact of relay 1200,'back contacts of relays 1251 and 814,

to ground on" the back contact of 'relay815. Relay 807 operates magnet 808 and this re lay and magnet release'in the same manner as relay 407 and magnet408, advancing switch 800 to the terminal marked by the grounding of conductor 440. lVhen brush 806 makes contact with conductor 440 a cir-v cuit is completed over the inner left back contact of relay 811, the Winding of relay 815 and battery Relay 815 in operating removes ground from the circuit of relay 807, preventing the advance of the master switch beyond the terminal connected to the conductor 440. It also closes a circuit from ground at its front contact through the Winding of relay 816 to battery. Relay 816 in operating connects the winding of relay 837 over its middle right contact,inner right contact of relay 810, brush 803, conductor 453, brush 404 to conductor 221 and thence to ground over the back contact of relay 220 and the front contact'of relay 218 thus operating relay 837 under the control ofrelay 218 Which is in turn under the control of the'sender 212. Relay 837 closes a circuit from batter 1 through the Winding of relay 821, front contact of relay 837 to ground at the left back contact of relay 1201. A circuit is closed in parallel with this through the left Winding of relay1203, back contact of relay 1204, conductor 1205 to the front contact of relay 837 so that relays 821 and 1203' are also under the control of relay 218. The operation of relay 1203 prepares a guard against ringing the Wrong subscriber in case of abandoned calls. Relay 821 in operating closes a circuit from battery through the Winding of relay 814, to ground at the left front contact of'relay 821. With relay 814 operated a circuit is closed from battery through the Winding of relay 822, inner left front contact of relay 814, right front contact of relay 821; to ground at the left back contact of relay 1201. Relay 822 in operating closes a. hold-' ing circuit for relay 814 at its outer right front contact.

The operation ofrelay 1200 which started the master switch in search of the group switch also closes a circuit over the inner right front contact of relay 1200 and the back contact of relay 1250 to operate certain relays in the position splitting circuit which in turn connect ground to conductor 1136. This ground completes a circuit over the right back contact of relay 1201, Winding of relay 817 and battery. With relay 817 op erated, a circuit is closed from battery through the Winding of relay 823, inner right front contact of relay 817, right front contact of relay 821 to ground at the hack contact of relay 1201. The operation of relay 823, which is an indication that the operator is ready to handle the call in connection with this master switch, closesa cir- Cult from ground at the inner right front contact of relay 823, inner right front contacts of relays 822 and 816.. inner left back contact of relay 810, brush 804, conductor 444 through the windings of relays 417' and 413 in parallel to battery. The operation of relay 417 extends the conductors 445, 447, 448, 450 and 452 to the group circuit. With relay 413 operated relay 411 is held operated in a local circuit and a circuit is closed for flashing lamp 414 which will he described hereinafter. Relay 817 also closes a circuit froinbattery through the Winding of relay 1202, inner left contact of relay 817 to ground in the sp it ing circuit over conductor 1133.

l-Vi r y 417 operated a circuit is closed to test Whether or not tae circuit for operating relay is properly closed. This circuit may be t ed from battery through the Winding of rel. y conductor 244, brush 406, Contact of relay 417, conductor 448 and conductor 855, right baclr contact of relay 237 through the winding ofrelay 824 to round in th record r circuit. If this cirit is properly completed relay oper- 245 do s not, due to thefresistates but relay ance of relay he operation of relay circuit for relay 826.

saw

824 closes an obvious Relay 826 locks over to ground at the front cont The operation of relay 826 from ground in the splitting elector 1133, the outerleft contact of relay 826, outer right contact of relay 817, outer left contact of relay 814, conductor 850, right normal contacts of relay 1221, Winding of relay 12h to ba tery. 'Relay 1218 discon nects the tip and ring conductors from the operators telephone and extends them to the secondary Winding of repeating coil 1222. Relay 826 also closes a circuit from ground at the outer i contact of relay 823, inner left contact of 826, left back contact of relay 827 back contact of relay 899 to conductor 1127 and thence to the splitting circuit to indicate that the home operator and'equipinent are busy With a call.

In addition, relay 826 closes a circuit from battery through-the winding of relay 1238, left back contact of relay 1237, inner right contact of relay 826 to ground at the outer right contact of relay 822. Relay 1238 in turn operates relays 1240 and 1239. These remain operated under the control of relay 1237 until the release key is operated. 0n ca ls incoming from dial oiiices the operation of relay 826 initiates operations which are eflectiveto prevent calls from being displayed if the plug of the associated tr nl; is still in the multiple jack from a previous call. Relay closes a circuit from battery throughthe left Winding of relay 832, middle left contact of relay 817, right normal contact ofrelay 818, resistance 1291, inner left contactof elay' 823, inner right act of relay 822. closes a circuit circuit over conits iiddle right contact contact of relay 826 to ground at the left contact of relay 821. Relay 832 closes an obvious circuit for relay 1290 and relay 1290 in turn operates relays 818 and 883. Relay 818 closes a locking circuit for itself over the back contact of relay 1289, left alternate contact of relay 818 to the operating circuit of relay 832. If the call is incoming from a n anual oiiice relay 1289 will be operated as will be described hereina .t z and the locking circuit of relay 8118 till be opened so that this testing circuit is only completed in the case of calls incoming from dial oliices. Relay 818 in operating disconnects the left winding of relay 882 from the contact of relay 826 and connects it over its right alternate contact to conductor 852 and thence over the inner upper front contact of relay 417, brush 105, conductor 22; to lamp 225 and hrough the winding of relay 229 to the sleeve of plug 228. If the plug has been left in the jack, ground will be connected to the winding of relay 229 and. relay 832 will be held operated. 1f the plug is not in the jack the operationof relay 818 opens the circuit of relay which releases in turn releasing relays 1290 and 888. \Vith relay 818 operated and relay 1290 released a. circuitis closed from ground the left contact of relay 821, inner right contact of relay 826, inner left contact of relay 823, inner right contact of relay 818, back contact of relay 1290 to conductor 1288.

The connection of ground to conductor causes the operation of a relay in the recorder circuit which prepares the recorder for receiving the call indicator pulses. This relay also connects ground in shunt of the winding of relay 821 thus operating relay 2 15 and releasing relay 8241. The operation of relay 2 15 disconnects the trunk from the windings of relay 21.8, causing relay 218 to release, in turn releasing relays 887, 821 and 1203 and thereby transmitting a signal to the sender 212 to cause it to send out the call indicator pulses. The operation of relay 245 connects he tip and ring conductors over conductors 2 17 and 24.6, contacts of relay 4117, conductors 1415 and 1:50, conductors 856 and 857, back contact of relay 1292 to the recorder circuit. The operation of the recorder is essentially the same as that described in U. 8. Patent 1,464,084 granted to A. E. Lundell et al., August 2, 1928.

The release of relay 821 above described does not release relays 826 and 81 1 since these relays are locked to the front contact of relay 822 and relay 822 is held operated over the front contact of relay 828, back contact of relay 829, outer right front contact of relay 826 to ground at the left baclr contact of relay 1201, this ground also holding relay 828 operated.

The operation of relay 826 as above described initiates the operation of the relay interrupter arrangement shown in the right 7 hand side of Fig. l. That is, the relay 826 closes a circuit from ground over the outer right contact of relay 822, inner right contact of relay 826, innermost lower contact of relay 1202, conductor 1208, winding of relay 1207, resistance 1206 to battery. Belay 1207 operates in turn operating relay 1209. Relay 1209 in turn operates relay 1210 and relay 1210. closes ground to resistance 1206 shunting relay 1207 and causing relays 1207, 1209, 1210 to release in succession. Relays 1207 and 1210 are slow to release to measure an interval before their release permits their reoperation. Relay 1209 also closes a circuit from ground at its left contact, normal contact and winding of relay 1211, resistance 1298 to battery. Relay 1211 operates and locks, and closes a circuit from grounded conductor 1208, alternate contact of relay 1211, winding of relay 1212, resistance 1297 to battery. Belay 1212 cannot operate being shunted by ground over the left contact of relay 1209. When relay 1209 releases this shunt circuitis opened and relay 1212 also operates. The next operation of relay 1209 closes a circuit from ground over its leftcontact. front contact of relay 1212, resistance 1298 to battery. This. circuit is in shunt of the winding of relay 1211 and that relay releases but relay 1212 is held operative over. the normal contact of relay 1211 to ground at the front contact of relay 1209. When relay 1209 releases the holding circuit of relay 1212 is opened-and that relay releases so that on the next closure of the contact of relay 1209 the cycle of operations is repeated. Each time that relay 209 operates ground. connected over its inner right contact to the winding of relay 1296. Each time that relay 1211 operates, which is half as often relay 1209, ground is connected to the winding of relay 1295. Ateach operation of relay 1296 ground is connected to conductors 1215 and 1216 and battery is removed from conductor 1294 while at each operation of relay 1295 ground is connectec. to conductor 121.3 and 1214 and battery is removed from conductor 1217. It will be apparent that this relay combination provides interrupted ground and battery at two rates, one twice as fast as the other. The operation of relay 817 which operates when the operator is ready to handle the call completes the flashing circuit for group lamp 11 1 which may be traced from battery through lamp 11 1, front contact of relay +113, conductor 167 through the splitting circuitto conductor 160, right back contact of relay 116, conductor 11-1. conductor 851, middle lower contact of relay 1202, right back contact of relay 828, conductor 1214: to ground at the right contact of relay .1295. It is therefore apparent that relay 114 will be intermittently lighted at the slow rate. At the same time a circuit is Rec closed from battery through lamp 225 which is individual to the trunk of Fig. 1,-conductor 224, brush 405, contact of relay 417,

contact of relay 1295. The trunk lamp 225 is therfore flashed at the slow rate as well. The operator is therefore given a visual indication of the group and trunk over which the call is incoming. A circuit in parallel with lamp 225 extends from conductor 852 over the middle left front contact of relay 817, left winding of relay 832 to battery. The currents through the two windings of relay 832, due to its di'lferentialwinding, neutralize one another and relay 832 remains unoperated.

The operation of relay 1218 above described in turn operates rela-y 1293. 4 Relay 1293 closes circuit from ground in the splitting circuit,over conductor 1134, right contact of relay 1293 to the Winding of relay 1219. Relay 1219 extends its operating ground to the winding-of relay 1220 and battery, while relay 1220 in turn operates relay 1221. Relays 1219, 1220 ancl 1221 are slow 0 operate these-arising a measured interval relays. Relay 1221 in operating opens. the circuit of relay 1218 and'rela-ys 1218, 1293;, 1219 and 1220 successively release. However relay 122-1 is held operated over its left alternate contact to ground over conductor.

850 as previously traced. The operation of relay 1218 connects the secondary winding of tone coil 1222 to condensers 1225 and 1226 and over front contacts of relay 1212 to the operators telephone set through the splitting lrcuit. Since relay 1292 is unoperated the tone circuit does not extend to the incoming trunk. The operation of relay 1293 closes a circuit through the primary of tone coil 1222, right normal. contact of relay 1219 to ground 1293. The operation of relay 1219 open-sthis circuit but the-operation of relay 1220 recloses it over the front contact of relay 1220. The operation of relay 1221 byrelea'sing relay 1218 andopening the secondary circuit of the tone coil 1222 t rm-inates the second impulse of tone. In consequence twoimpulses of tone are transmitted to the condensers and through them to the operators headset. This calls the attention of the operator to the fact that a callis awaiting her attent should she fail to observe thelighting of lamp 414- or of lamp 225.

Relays 82? and 828 whenoperated'conncct lar a causing the lamp tobe flickered the higher speed. These relays are only o erated ifthe operator handling the call r to elapse between the operation of successive.

at the left front contact ofrelay' 225 and 41'4-with the contacts of is the teamoperator and not the home operator. I 7

Following the reception of the last'pulse of the designation, the circuit of relay 245 is opened to cause the transfer of the tip and ring conductors hack to the windings of relaylQlS and the sender 212 advances the district selector to talking position.- A' cir cuit is also prepared from the recorder circuit to conductor 836, outer left front con-- tact of relay 817, back contact of relay833, left winding of relay 835 to battery preparing for the o eration of the release key. In addition a circuitis closed from ground in the recorder circuit over conductor 921 to the winding of relay 1204 and the armature of relay 1203. V

When the district selector 213' has advanced to talking position, relay 218 re operates in series with a relay in the selector circuit, again'groundingconductor 221 and reoperating relay 837 which in turn reopeates relays 821 and'1203. If the call indicator circuit has grounded conductor 921 at :the'

time that relay 1203. reoperates, a circuit is closed from battery throughthe winding of relay 1231, outer left contact of relay 1203 to conductor 921. Relay 1231 looks over its front contact through the winding of relay 1204 to conductor'92l but relay 1204 is inoperative since ground is connected to both terminals of its winding. The purpose of relay 1204 is to prevent, ringingthe wrong party if reselection takes place quickly after abandonment. If the call should be abandoned at this time, relay 1203 would release and remove ground from the second terminal of relay, 1204 permitting that relay to operate in the locking circuit of relay 1231. 1 V ith relay 1204 operated it'is impossible forrelay 1203 to reoperate and hence to com-1 plot-e the circuit for starting the ringing of its right winding and right front contact to ground at the front contact of relay 814. ,It

also closes a clrcuit f"om ground over its left contactv to the WlDClID of rela 1235 and tothe inner left contact of relay 1203 providing' a locking circuit for'that rela-y. In

addition, it extends its locking ground to the right winding of relay 1234 which re lay looks through its left winding and left front contactunder the control of the release key, rendering' the release independent ifs of the length of time that the release key is held operated.

Relay 1235 in operating closes a circuit from battery through the winding of magnet 408, conductor 451, brush 801, right back contact of relay 838, outer left contact of relay 1235 to ground. It also closes a circuit fromground over its outer right contact, front contact of relay 1 203, middle left contact of relay 826, inner left back contact of relay 833, conductor 452, contact of relay 417, brush 403, conductor 226, winding of relay 220 to battery. A third circuit extends from ground over its inner right contact, the winding of relay 1237 to battery, and in parallel therewith over the front contact of relay 1203 to the winding of relay 1201 and battery. A fourth circuit extends from ground over the innerleft contact of relay 1235, winding of magnet 808 to battery.

Relay 1237 in operating opens the circuit of relay 1238 which releases, in turn releasing relays 1240 and 1239. Relays 1238 to 1240 release slowly, completing after an interval a circuit from ground over the normal contact ,of relay 1238, back contact of relay 1239, front contact of relay 1237 to the winding of relay 1201. An alternate circuit for operating relay 1201 is therefore provided in case the district selector is slow in. closing the talking circuit thus delaying the operation of relay 1203.

The operation of relay 1201 opens the cir cuit of relays 817 and 821. Relay 817 releases relay 1202 thereby disconnecting the operators telephone from this master circuit, opens the flashing circuit for lamp 414, the operating circuit for the relay interrupter and the operating circuit for relay 823. Relay 823 in turn releases relays 417 and 413 disconnecting the group circuit from and releasing relays 815 and 813. Relay 823 also releases relay 822 and that relay in turn releases relay 814, which finally releases relay 835. The release of relay 835 releases relay 1235 which in turn releases magnet 808 and permits the advance of the master switch to itsnext terminals where it will serve any call which may eXist in the corresponding group before advancing to other groups. The release of relay 1235 also releases magnet 408 to advance switch 400 to the next trunk thus definitely opening the conection between the trunk and the group circuit. 7

The master switch isnow ready to serve a call in the next group. If such a call is waiting, it will hold relay 1200 o erated and reoperate relay 815 to initiate t e operation of the master switch circui If a call is waiting in some other group the operation of relay 815 will be delayed until the master switch has been advanced to the corresponding terminals. I

Relay 220 when operated under the control of relay 1235 and 1203 as above described the master circuit locks to ground at the front contact of relay 218 and prepares for ringing the called subscriber. The operator tests the called line jack with the tip of the trunk plug, the test circuit extending from the sleeve of jack 227, tip of plug 228, upper back contact of relay 229, back contact of relay 230, conductor 233 to the operators headset through the splitting circuit. If the called line is idle, the operator inserts plug 228 in jack 227, completing a circuit from ground through the cutoff relay of the subscribers line, sleeve of jack 227 andplug 228, winding of relay 229, to battery through lamp 225. Lamp 225 does not light since relay 229 immediately operates closing a circuit from battery through the winding of relay 238, back contact of relays 237 and 236 in parallel with the winding of relay 237, lower front contact of relay 229, outer right contact of relay 220. winding of relay 229 to ground on the sleeve of the line. Relay 238 operated closes a circuit from source of ringing current 239, winding of relay 236, lower front contact of relay 238, ring of plug 228 and ack 227 through the ringer at the subscribers substation over the tip of jack 227 and plug 228, upper fro-nt contact of relay 229, upper front contact of relay 238 to ground. The subscriber is signaled over this circuit. Relay 236 does not respond to ringing current, but when the called subscriber answers, the direct current circuit provided causes the operation of relay 236 which opens the shunt around the winding of relay 23' Relay 237 then operates looking to battery at its own front contact and shunting relay 238 which releases to connect the tip and ring of the subscribers line through to the right windings of repeating coil i219. Relay 240 now operates closing a circuit from ground over its front contact, outer left front contact of relay 220, winding of relay 248 to battery.

Relay 248 reverses the connection of battery to the tip and ring conductors to the district selector for supervisory purposes. Relay 220 remains locked to relay 218 as long as the calling subscriber keeps his receiver off the switchhook.

When the called subscriber hangs up, relay 240releases in turn releasing rel y 248 and restoring the directionof current in the trunk; Vhen the callingsubscriber disconnects, relays 218 and 220 release and he shunt around lamp is opened, permitting that lamp to light in series with the winding of relay 229 as long as the plug 228 remains in thejack. If the operator should inadvertently remove the plug from the jack 905 from ground the contact of still lighted as above described inseries with the sleeve relay 229. Theoperation of the group circuit and the master switch is tie same as described above. relay 26 operates and initiates the operation of the interrupter relaysfor the purpose of flashing lamps 414 and 225, a circuit is closed from battery through the left winding of relay 832, middle leit contact of relay 817, outer right contact of relay 818, conductor 852 and thence over conductor 447, contact of relay 417, brush 405, conductor 224 to the winding of relay 229. Ground is now connected to this winding and conductor 224 from the sleeve of jack 227. At this time no current flows through the right wind ing of relay 832 since one side of this winding extends to ground. over conductor and the other to groundover the back contact of relay 833 previously traced. The currents through relay 832 are tllQP-Bi re unbalanced and relay operates, in turn operat 0024 relays 1290 and 833 as above desc Relay 833 in operating transfers the rig t winding oi? relay 832 from ground 0* er con ductor1213 to battery over the back contact of relay 827 and the left back contact of relay 1211. Relay 1211 therefore intermit tently connects battery through the right winding of relay 832 to conduct-or 224 in shunt of lamp 225, extinguishing that lainp at intervals to give a flashing signal to operator. The direction of this intermittent current through the right winding of relay 832 aids in holding the relay operated. It is impossible for the operator to disconnect the pos tion equipment from the trunk without removing the plug from thejack, since the operation otrelay 833 opens the circuit from the release key to relay 835. The

removal of the plug from the jack causes the release of relays832, 1290 and 833 permitting the operator to release her position equipment and to complete the call in the usual manner. Since rel y 83.5 and therefore relay u as the plug s in the j ack relay 220 cannot be operated and it is impossible to ring the wrong subscriber. If the sleeve of a trunkshould become 1235 cannot be operated as 10 7 grounded. relays 832 and 833 cannot be released by the removal of the plug from a line jack, and the release keys are ineffective.

In this case the emergency release key 1242 This key closes a. circuit 12 ett may be operated.

ba k contact of relay 1241, left winding of relay to battery. Relay 841' operates relay 835 which performs its releasin functions. Relay 841 locks to, the contact or relay 814 and operates relay 1241which locks as long as key 1242 is held operated.

If neither the release key 1232 or 1233 nor the emergency release key 1242 will. release the position equipment, the emergency key 890 is operated. Key 890 closes obvious cirowe ver, when operat ors telephone.

part of Fig. 1. The original operating cirv cuit for relay 118 extends only through its left winding and the supervisory circuit controlled by relay 140 closes the circuit through the right winding of relay 118, instead of operating relay 148 which is inefiective and might have been omitted altogether. In ad- 7 dltion the incoming tip and ring conductors are connected directly to the armatures of relay 148-instead ot over the back contacts of relay 145 so thatthe operation of relay 145 to associate the operators telephone with the trunk does not open the circuit of relay 118..

A call originating at a manual oihce will be extended by means of a cord circuit (not shown) to a trunk of the modified form of Fig. 1. Switch 400 and switch 800 will be associated with the trunk in the manner described for a call from a dial oflice. Trunks incoming from a manual office are marked in the'bank of brush 401 by ground. As soon as relay 816 operates this round extends over brush 401, conductor 405, brush 802, outer right contact of relay 810, outer right Contact of relay 816, winding of relay 829 to battery. Relay 829 operates, in turn operating relay 1289 and relay 1292. Relay 829 at its outer right front contact connects the release keys 1232 and 1233 to the winding of relay 835 under the control of relays 817 and 833. This renders the release key effective at any time following the operation of relay823 which is opera ted over the splitting circuit immediately after the operation of relay 1200. Relay 829 also opens the circuit by which relay 823 is held operated in the case of an abandoned dial call under the control of the release key, so that an abandoned call from the manual othce will release the master circuit autoinati cally.

Relay 1289 operates relay 818 and together with relay 818 connects ground to conductor 1-288, cancellingthe test of the trunk plug. Relay 1292 transfers the tip and ring conductors from the recorder circuit to the armatures of relay 1218 and thence to the proceed in the manner described for a call from a' dial oiiice except that the Wanted num her is passed orally from one onerator to the other instead or" by call indicator impulses.

As soon as the operator has received the number she operates the release key, operating relay 835 and advancing the group and master circuits, and setting the ringing by operating relay 220 as above described.

The operations now gacl-z.

Althoughthe operation of relay 829 renders the release key effective at any time during straightforward calls, this 33 is ineil ective whenever the trunk plug is in a multiple It will be remembered l at relay 818 is operated directly by relay 1289 or through the operation of relays 832 and 1290 in response to the prepared by relays 826 and 823. With relay 81S operated the left winding or i ay 8-32 connects over the middle left contac' of relay 817, right alternate contact 0" rel =v 838, to conductor and thence to and relay lit the plug is in the 832 either operates or is held op- J'oin ground supplied from the sleeve r and in turn either operates or holds operated relay 1290. l i ith relay 1290 operated circuit is closed for relay 833 which opens the operating circuit for relay 835.

If, on a dial call, the recorder fails to operate properly to bring about a complete display of the wanted number the release circuit is not closed and the position must be released by the operation of the emergency release lrey 1242. Before doing so however, the operator may obtain the number from the calling subscriber by operating key 128? which operates relay directly, connect ing the trunk through to the operatofis telep ions. The sen r at the oistant end, having finished transrn ;ing the number, causes the district selector 213 to prepare the talking circuit and the erator is therei'ore connected through to the calling subscriber.

If for any reason the circuit of relay 2% fails to close, for example, because of a poor contact between brush 4% and the terminal connected to conductor 24%, the number will not be di layed since no signal. will be transmitter t one sender to cause it to star transmi he designation. 'lhereroreii the number uoes not appear on the recorder in the usual len th of time following the tone indicating that a call is incoming, the operate: will release the master circuit by opcrating the emergency release hey 1242. With the circuit oi relay open relay 82 1 cannot operate and in turn relay fails to operate: The operation of emergency release key 12 operates relay which turn operates relay 1235 and 1201. Relay 1203i nas be n held operated under the control of relay which in turn was held coniously operated from relay 218. However, si* :e relay 826 doesnotoperate relay 220 can n t be operated. The advance of the group sr vch 4G0 and the ma or switch 800 under the relay 122w opens the circuit What is claimed is:

1. In a telephone system, an incoming trunk line, an operator s position, equipment at said position, automatic switching means for connecting said equipment with said trunk line, means to disconnect said equipment from said trunk line, and means to cause a second connection between said trunk line and said equipment if said first connection is not effective.

2. In a telephone system, incoming trunk lines, an operators position, equipment at said position, switching means at said position, means responsive to the seizure of a trunk line to cause said switching means to connect with said trunk line, means responsive to said connection to establish a circuit between said trunk line and said equipment, means to disconnect said switching means from said trunk line, and means to cause Witching means to again connect with said trunk line if said circuit is not efiectively established.

3. in a telephone exchange system, atrunk line, an operators position, apparatus at said position, means responsive to the seizure of said trunk line for applying a calling condition to said trunk line, means responlive to said calling condition to associate trunk line with said position apparatus and to remove said calling condition, and means to restore said calling condition to said trunk lineif the association of said trunk line with said apparatus not eilective.

In a telephone exchange system, an operators position, a trunk line appearing at position, apparatus at said position, neans responsive to a. seizure of said trunk he to apply a calling condition thereto, neans responsive to such calling condition to cause said apparatus to hunt for said trunk line, means to establish a circuit to in form the operator of the wanted subscribers designation, operator controlled means to disconnect said apparatus from said trunk, and means effective if said circuit is not established and responsive to said operator controlled means to restore the calling condition to said trunk line.

5. In a telephone exchange system, an operators position, a. plurality of trunks appear at said position, apparatus at said position, means responsive to the seizure of said trunk to apply a calling condition there to, means resoonsive to the existence of said calling condition on any trunk to cause said apparatus to hunt for a trunk on which said cond tion exists, means to establish a circuit connecting the trunk found and said apparatus inform the operator of the called line designation, operator controlled means to disconnect said apparatus from said trunk and cause said apparatus to hunt for another trunk on which a calling condition exists,

and means eiiective'if said circuit is not es tablished and responsive to said operator controlled means to restore the calling condition to said trunk.

6. In a telephone exchange system, an operators position, a plurality of trunk cir-' cuits appearing at said position, a recorder at said position, means responsive to the seizure of said trunk circuits for applying a calling condition thereto, switching means responsive to said calling condition tosuccessively associate said recorder with trunk circuits to which said calling condition has been applied, means to establish a recording circuit between said recorder and the trunk circuit with which it is associated, operator controlled means to disconnect said recorder from said trunk, and means effective if said recording circuit is not established to restore said calling condition to said trunk.

7. In a telephone exchange system, an operators position, a trunk line appearing at said position, a called line recorder, means responsive to the extension of a call to said trunk line to cause said recorder to associate itself with said trunk line, operator controlled means for disconnecting said recorder from said trunk line, means normally responsive to said operator controlledmeans to prepare the trunk line for ringing the wanted subscriber, andmeans effective if the association of said recorder with said trunk line is not eiiective to prevent the preparation of ringing andto restore the calling condition to said trunk line, whereby a suban operators position, a plurality of plug-ended trunks appearing at said position, a plurality of jac s to outgoing lines, a recorder at said position, means responsive to the seizure of a trunk to establish a connection between said recorder and said trunk, means to delay the establishment of said connection as long as the plug of the trunk is in one of. said jacks, operator controlled means for preparing the signaling means of said trunk to signal the designated outgoing line, and means to render said operator controlled means inefiective to prepare said signaling means ifsaid connection is not established.

In witness whereof, I hereunto subscribe my name this 24th day of September, 1930.

ALBERT C. POWELL.

sequent attempt may be made to associate the recorder with the trunk line.

8. In a call distributing system, an operators position, a plurality of plug-ended trunks appearing at said position, a plurality of jacks extending to outgoing lines, a plurality of switching devices at said position, a recorder at said position, means'responsive to the seizure of a trunk to cause a plurality of said switching devices to associate themselves with said trunk, means automatically responsive to said association to connect said recorder with said trunk-to receive the designation of an outgoing line, and means to prevent the connection of said recorder with said trunk if the plug of the trunk is in one of said jacks.

' sponsive to the seizure of a trunk to automatically associate said trunk with said designation receiving means, means to discriminate between said trunks incoming from a manual oflice and saidtrunks incoming from 

